This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-127872 filed on Apr. 27, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to vehicle brake systems. More particularly, the present invention pertains to a brake control device provided with a brake pedal behavior simulator and a brake pressure control device. The invention also pertains to a brake control device having the brake pressure control device arranged to carry out an anti-skid control or other braking controls such as sudden braking.
A known brake control device is disclosed in U.S. Pat. No. 4,989,925 issued on Feb. 5, 1991. The disclosed brake control device includes a master cylinder for generating hydraulic pressure in proportion to a brake pedal operation force, a wheel cylinder (wheel brake) connected with the master cylinder by a main conduit (hydraulic passage), a brake pedal behavior simulator (absorber) disposed at the end of a branch conduit branching from the main conduit, a brake pressure control device, and an electromagnetic valve (control valve). The brake pressure control device is connected with the main conduit between the branch point and the wheel cylinder and is provided with a pressure source. The brake pressure control device applies hydraulic pressure generated by the pressure source and is activated for the purpose of increasing, decreasing and/or maintaining hydraulic pressure in the wheel cylinder. The electromagnetic valve is disposed at the branch point and is activated for establishing and interrupting fluid communication between the master cylinder and the wheel cylinder. When the brake pressure control device is normally operated, the electromagnetic valve functions for establishing the fluid communication between the master cylinder and the brake pedal behavior simulator. On the other hand, when the brake pressure control device malfunctions or is abnormally operated, the electromagnetic valve functions for establishing the fluid communication between the master cylinder and the wheel cylinder.
As described above, the known brake control device includes the electromagnetic valve which changes fluid communication between the master cylinder and the wheel cylinder to fluid communication between the master cylinder and the brake pedal behavior simulator or vice versa in response to the condition of the brake pressure control device. With this type of brake pressure control device, the hydraulic pressure in the wheel cylinder is controlled by the brake pressure control device when the brake pressure control device is normally operated. However, only when the brake pressure control device malfunctions or is abnormally operated, the hydraulic pressure in the wheel cylinder is controlled by the hydraulic pressure from the master cylinder in proportion to the brake pedal operation force.
The brake control device provided with the above-described components and operational characteristics may suffer from several drawbacks, The electromagnetic valve is switched over after initiation of the brake operation is detected by a stroke sensor (pedal effort sensor). Therefore, the known brake control device requires that the electromagnetic valve have sufficiently large suction power capable of opposing the master cylinder hydraulic pressure generated by the brake pedal operation. Further, the electromagnetic valve used in the known device is required to have a high responsiveness so that the driver feels comfortable with the brake pedal operation even during an emergency braking operation. Accordingly, the size and cost associated with the electromagnetic valve are increased.
A need thus exists for a brake control device that permits the electromagnetic valve to be downsized while also minimizing the cost associated with the electromagnetic valve.
According to one aspect of the invention, a brake control device includes a master cylinder for generating a hydraulic pressure in proportion to a brake pedal operation force, a wheel cylinder connected with the master cylinder by a main conduit extending from the master cylinder, a brake pedal behavior simulator disposed at the branch conduit branching from the main conduit, a normally-open type electromagnetic valve, a normally-closed type electromagnetic valve, and a brake pressure control device that includes a pressure source. The normally-open type electromagnetic valve is disposed in the main conduit between a branch point of the branch conduit and the wheel cylinder, and establishes and interrupts fluid communication between the master cylinder and the wheel cylinder. The normally-closed type electromagnetic valve is disposed in the branch conduit and establishes and interrupts fluid communication between the master cylinder and the brake pedal behavior simulator. The brake pressure control device is connected to the main conduit between the normally-open type electromagnetic valve and the wheel cylinder, and is provided with a pressure source. The brake pressure control device applies hydraulic pressure generated by the pressure source for the purpose of increasing, decreasing, and maintaining hydraulic pressure in the wheel cylinder. When the brake pressure control device is normally operating, the wheel cylinder hydraulic pressure is controlled by the brake pressure control device, with the normally-open type electromagnetic valve being closed and the normally-closed type electromagnetic valve being opened. When the brake pressure control device malfunctions and is abnormally operating, the wheel cylinder hydraulic pressure is controlled by the master cylinder hydraulic pressure in proportion to the brake pedal operation force, and the normally-open type electromagnetic valve is opened and the normally-closed type electromagnetic valve is closed. The reference to malfunctions of the brake pressure control device defines that the pressure source is not actuated to generate a desired hydraulic pressure. Accordingly, the hydraulic pressure for the brake control operation is decreased. Additionally, at least the normally-closed type electromagnetic valve is operated for opening when the brake pedal is in a non-operational state. The reference to the non-operational state of the brake pedal defines that the brake pedal is not applied or the brake pedal is applied with little brake pedal operation force. Accordingly, when the brake pedal is in the non-operational state, the hydraulic pressure from the master cylinder is equal to or lower than a predetermined value.
In the brake control device of the present invention, the normally-closed type electromagnetic valve functions for establishing and interrupting fluid communication between the master cylinder and the brake pedal behavior simulator. The normally-closed type electromagnetic valve is opened only when the brake pedal is in the non-operational state. Therefore, the normally-closed type electromagnetic valve is operated so as to be opened without hydraulic pressure being generated in the master cylinder. Accordingly, the normally-closed type electromagnetic valve is not required to have an extremely large suction power to switch the valve against the master cylinder hydraulic pressure in proportion to the brake pedal operation force. As mentioned above, the normally-closed type electromagnetic valve is operated for opening when the brake pedal is in the non-operational state. Therefore, the normally-closed type electromagnetic valve of the present invention is not required to have a high responsiveness not only when the normal brake is applied but also when a sudden brake is applied. Accordingly, with the brake control device of the present invention, it is possible to downsize the normally-closed type electromagnetic valve and lower the manufacturing cost.
It is quite advantageous that the normally-open type electromagnetic valve for establishing and interrupting fluid communication between the master cylinder and the wheel cylinder is operated for closing when the brake pedal is in the non-operational state as well. Accordingly, the brake control device of the present invention permits a reduction in size and manufacturing cost not only for the normally-closed type electromagnetic valve but also for the normally-open type electromagnetic valve.
According to another aspect of the invention, a brake control device for a vehicle includes a master cylinder for generating a hydraulic pressure in proportion to a brake pedal operation force, a main conduit extending from the master cylinder, a wheel cylinder connected to the master cylinder by the main conduit, a branch conduit branching from the main conduit, a brake pedal behavior simulator disposed at the branch conduit, a first electromagnetic valve disposed in the main conduit between the branch conduit and the wheel cylinder for establishing and interrupting fluid communication between the master cylinder and the wheel cylinder, and a second electromagnetic valve disposed in the branch conduit for establishing and interrupting fluid communication between the master cylinder and the brake pedal behavior simulator. A brake pressure control device is connected to the main conduit between the first electromagnetic valve and the wheel cylinder, and includes a pressure source. The brake pressure control device increases, decreases, and maintains hydraulic pressure in the wheel cylinder by hydraulic pressure generated by the pressure source, with the hydraulic pressure in the wheel cylinder being controlled by the brake pressure control device so that the first electromagnetic valve is closed and the second electromagnetic valve is open when the brake pressure control device is normally operating, and with the hydraulic pressure in the wheel cylinder being controlled by the hydraulic pressure from the master cylinder in proportion to the brake pedal operation force so that the first electromagnetic valve is open and the second electromagnetic valve is closed when the brake pressure control device is malfunctioning. In addition, the first electromagnetic valve is closed only when the brake pedal is in the non-operational state.
In accordance with another aspect of the invention, a brake control device for a vehicle includes a master cylinder for generating a hydraulic pressure in proportion to a brake pedal operation force, a main conduit extending from the master cylinder, a wheel cylinder connected to the master cylinder by the main conduit, a branch conduit branching from the main conduit, a brake pedal behavior simulator disposed at the branch conduit, a first electromagnetic valve disposed in the main conduit between the branch conduit and the wheel cylinder for establishing and interrupting fluid communication between the master cylinder and the wheel cylinder, and a second electromagnetic valve disposed in the branch conduit for establishing and interrupting fluid communication between the master cylinder and the brake pedal behavior simulator. A brake pressure control device is connected to the main conduit between the first electromagnetic valve and the wheel cylinder, and includes a pressure source. The brake pressure control device increases, decreases and maintains hydraulic pressure in the wheel cylinder by hydraulic pressure generated by the pressure source. The hydraulic pressure in the wheel cylinder is controlled by the brake pressure control device, with the first electromagnetic valve being closed and the second electromagnetic valve being open when the brake pressure control device is normally operating. The hydraulic pressure in the wheel cylinder is controlled by the hydraulic pressure from the master cylinder in proportion to the brake pedal operation force, with the first electromagnetic valve being open and the second electromagnetic valve being closed when the brake pressure control device is malfunctioning. The second electromagnetic valve is opened only when the brake pedal is in the non-operational state and the first electromagnetic valve is closed only when the brake pedal is in the non-operational state.